You can use dedicated snow filters or particle systems to create snow that can be either stylized or realistic. There's filters built into After Effects like CC Snow, CC Particle World, and Particle Playground -- or you can use 3rd-party filters like Trapcode Particular (which is AE 3D camera-aware), Boris FX Snow, Cycore FX HD Snowfall, DigiEffects Delirium Snow, and GenArts Monsters GT.
You can use dedicated snow filters or particle systems to create snow that can be either stylized or realistic. There's filters built into After Effects like CC Snow, CC Particle World, and Particle Playground -- or you can use 3rd-party filters like Trapcode Particular (which is AE 3D camera-aware), Boris FX Snow, Cycore FX HD Snowfall, DigiEffects Delirium Snow, and GenArts Monsters GT.
GenArts just announced Monsters GT for the Mac, with over 50 effects including a variety of stylize, distort effects, fluid, trail, and particle effects. A Windows version is also available for CS5 & CS4.
PVC has a nice review of this filter set by Kevin P McAuliffe. [update: see also his Review - Genarts Sapphire v5 for Adobe’s After Effects] Monsters GT has floating point support, and the fluid simulation filters especially will benefit from GPU optimization, supported at the maximum in NVidia GeForce 200 or 400 series or Quadro 5800. Many of these are unique filters from the Flame and Smoke world, though some are similar to other AE filters. Monsters GT was acquired in the purchase of SpeedSix, adding to GenArts stable of AE filter sets that include Sapphire, Tinder, and particleIllusion. Monsters GT features these tools:
Stylize effects such as CCTV, NightVision and Brush
Warps and distort effects such as HeatHaze, Puddle and Ripple
Particle effects such as Rain, Smoke and Snow
Fluidz, a set of plug-ins that use the power of 2d fluid dynamics to create Fire and fluid flow simulations (was in Raptors)
Trailz, a set of plug-ins that create a variety of smooth, particulate and stop-motion trails (was in Raptors).
Here's an overview, plus a demo of the Aurora (Autodesk version), which generates images similar to Trapcode Form:
Red Giant has a new After Effects video tutorial, Creating a Looping Particle System (episode 3), that uses both Trapcode Particular and Starglow to create a looping, stylized holiday snowstorm. Host Aharon Rabinowitz already did a looping particles tutorial at Creative Cow (with built-in CC Particle System II), but this apparently goes deeper.
In the same vein, Motionworks has a free project Particular: Snowflakes, and in Layers TV: Episode 67guest Jason Scrivner demonstrates for beginners how to create falling snow flakes with Particle Playground.
The Boris Continuum Complete Snow filter for Apple Final Cut Pro and Motion is free until March 1st. It's an auto-animated snow generator with extensive options that allow you to create drifts or make flakes pile up along the edges of an alpha channel.
Download the free Snow filter here, and look at the tutorial too. You must install the free BCC Fxplug before March 1, 2008.
There's also a free "blizzard" effect from DVCReators.net.
You can use dedicated snow filters or particle systems to create snow that can be either stylized or realistic. There's filters built into After Effects like CC Snow, CC Particle World, and Particle Playground -- or you can use 3rd-party filters like Trapcode Particular (which is AE 3D camera-aware), Boris FX Snow, Cycore FX HD Snowfall, DigiEffects Delirium Snow, and GenArts Monsters GT.
Also posted recently at PVC was the mini-roundup Animate a Photo Mosaic in After Effects.
